This invention relates to a high-speed etching apparatus for use in the manufacture of electrical parts such as semiconductor integrated circuits.
The miniaturization of integrated circuits has made such rapid progress in the last few years that recently very large scale integrated circuits (VLSTs) have been developed with dimensions of 1-2 .mu.m. For such minaturization, a method that has attracted attention is the Reactive Ion Etching method or RIE, wherein a reactive gas, such as CF.sub.4 or CCl.sub.4, is introduced into a decompression or vacuum vessel having parallel-plate type electrodes; glow discharge is produced by applying radio frequency electric power to the electrodes on one of which the sample to be etched has been placed, and etching is effected by accelerating the positive ions in the plasma by means of the negative DC self-bias (cathode voltage drop) produced at this electrode, irradiating the sample vertically.
In this RIE method, however, when etching SiO.sub.2 using CF.sub.4 +H.sub.2 gas, for example, the etching rate was at most 300-400 A/min, which meant that it took twenty to thirty minutes to etch a 1 .mu.m SiO.sub.2 film. Etching speed was also slow in the case of Al and poly-Si, and the method is ill-adapted for mass production. It is known that increasing the operating current is effective, but this brings with it the danger of an increase in the cathode voltage drop, with the risk of ion damage to the sample and a decrease in the etching selectivity radio, which is the ratio of the etching rate of the layer being etched (such as SiO.sub.2) to the etching rate of the substrate (for example, Si). Another limitation was that the resist material used to mask the surface reached a high temperature and became subject to deformation.
The present inventors previously developed a high-speed RIE method for etching monocrystalline Si, SiO.sub.2, Al, Mo, W, and poly-Si without any risk of ion damage which is described in full detail in U.S. patent application Ser. No. 324,663, filed on Nov. 24, 1981, by the same inventors as those of the present invention. In this method a magnetron discharge is used for etching by applying a magnetic field perpendicular to the electric field between the parallel electrodes within a reaction chamber in the decompression vessel where a reactive gas, CF.sub.4 mixed with H.sub.2, is introduced for ionization.
According to the parent applications, an apparatus and method for dry etching are disclosed in which an etchant gas such as CF.sub.4 +H.sub.2 is introduced into a reaction chamber; high-frequency electric power is applied between the upper wall of the reaction chamber, which acts as an anode, and a cathode of nonmagnetic metal within the reaction chamber. A magnet assembly under the cathode generates a magnetic flux B perpendicular to the electric field E (caused by the cathode voltage drop) in the vicinity of the upper surface of the cathode. Electrons in the electromagnetic field are accelerated by the force E.times.B so that they are trapped in a drift track and generate a magnetron discharge within the discharge area, near the upper surface of the cathode. A sample to be etched, such as a semiconductor wafer, is placed on the surface of the cathode; and the magnet assembly under the cathode is enclosed in a shield room which is made of insulating material such as "Teflon" in order to prevent any discharging below the cathode. The apparatus enables etching to be done at high rates such as more than 6000 A/min for SiO.sub.2. The improved method of application No. 373,162 involves the use of reactive gas molecules which contain atoms of both fluorine and hydrogen, in the same type of apparatus, to improve the etching selectivity ratio. The apparatus, however, has a problem in that the magnetron discharge occurs not only in the discharge area but also in the shield room because the atmosphere inside the shield room communicates with, and is kept in the same condition as, that in the discharge area which is evacuated and supplied with reactive gas at a pressure of about 10.sup.-4 Torr. The discharge in the shield room results in about twice the power consumption as is require to etch the sample. Moreover, the discharge in the shield room heats the cathode and injures the resist material provided as a patterned mask on the sample.